1. Field of the Invention
The present invention relates to reporting in a cellular communication system, and in particular, but not exclusively, to reporting of measurement results from a transceiver station to the communication system.
2. Description of the Related Art
A wireless communication network may comprise a cellular radio network consisting of cells. In most cases a cell can be defined as a certain area covered by one or several base transceiver stations (BTS) serving mobile stations (MS) within the cell via a radio interface. The base station may be connected to a base station subsystem (BSS). Several cells may overlap and cover together a larger area, thereby forming the coverage area of a cellular radio network. The cell (or group of cells) and thus the mobile station (MS) or similar user equipment (UE) within one of the cells of the system can be controlled by a node providing controller functionality. Examples of the network controller include a base station controller (BSC), a radio network controller (RNC) and a mobile switching center (MSC), but other control nodes may also be used. The controller can be connected further to a gateway or linking node, for example a gateway GPRS support node (GGSN) or gateway mobile switching center (GMSC), linking the cell to the other parts of the communication system and/or other communication networks, such as to a PSTN (Public Switched Telecommunications Network) or to a data network, such as tc a X. 25 based network or to a TCP/IP (Transmission Control Protocol/Internet Protocol) based network. The cellular telecommunication networks typically operate in accordance with a given standard (or several standards) which sets out what the elements of the network are permitted to do and how that should be achieved. Examples of the cellular telecommunications network standards include code division multiple access (CDMA) based standards (such as the Digital Advanced Mobile Phone Service (DAMPS), or Wide-band CDMA or the proposed Universal Mobile Telecommunications System (UMTS) or time division multiple access (TDMA) based standards (such as GSM: Global Standard for Mobile or the GSM based General Packet Radio Service (GPRS)) or frequency division multiple access (FDMA) based standards. In addition to basic voice and data communication services, the users of the mobile stations are provided with various other services known to the skilled person.
The mobile station and/or the base station may measure and/or define several parameters concerning the conditions in the cell, such as signal levels (power) between the receiving and transmitting stations, quality of the signal, distance between the stations, amount of transmitted data and so on. The mobile station can be provided with appropriate means for defining a value for any parameter that can be measured for the interaction between the mobile station and any of the base stations or the conditions in a cell. The measurements or definitions performed by the mobile station will be referred to in the following as cell measurements and the results obtained by the mobile station will be correspondingly referred to as cell measurement results.
During an ongoing call the mobile station may report to the network controller so called neighbouring cell measurement results associated with cells neighbouring the cell serving the mobile station at the current moment by a measurement result message. In other words, the neighbouring cells can be defined to be the other cells of the system than the cell currently serving the mobile station. For example, in the GSM based systems the reporting may be done on SACCH (Slow Associated Control Channel). In this instance the measurement result message consists of information related to the serving cell and also information concerning the six strongest neighbouring cells. In the GSM based systems the report message frame includes information bits for the measured RXlevel (received signal level), BCCH-frequency (Broadcast Control Channel frequency) and the BSIC (Base Station Identity Code) for each reported neighbouring cell. At the current GSM based systems the RX-level is reported with six bits. The value range of the information is set to be from −47 dBm to −10 dBm with 1 dB steps.
In the current measurement reports it is possible to report only six neighbouring cells in maximum. Since the number of the cells with which the mobile station may interact can be greater than this it could be advantageous to have a report covering more than only the six cells. This is especially the case in multisystem or multiband networks and/or in cellular communication systems operating in a multilayer environment. In general, the multimode systems can be defined as a communication environment in which the mobile station may be in a such service area where it may be served by more than one serving network or system or standard or frequency and so on. An example of a multiband system is a dual-band GSM mobile stations served by both 900 MHz and 1800 MHz frequencies. An example of a multisystem is a dual mode telephone operating e. g. in GSM networks and in UMTS networks.
For example, in the current GSM standard a reported neighbouring cell will reserve 17 bits from the reporting message. There is no free space in the current measurement report message to include more cell measurement results for the neighbouring cells than said measurement results for six neighbouring cells.
In addition, the reporting of the RX-level with 6 bits only may cause limitations in the reporting range in some applications. Especially, the maximum value of the indicated RX-level may be insufficient for all applications. Therefore it could be advantageous to be able to indicate RX-levels that are higher than the currently possible levels, such as the −47 dBm maximum value. Reports of higher received signal levels is needed e. g. for the purposes of handover decisions in instances where the mobile station is close to a sectored base station and moving from one sector to another sector of the base station.
Furthermore, at signal levels above e. g. −47 dBm value, the current measurement report cannot indicate if the serving cell has a higher power than one of the neighbouring cells unless the serving cell is included in a list of the neighbouring cells. This approach is, however, not a desired solution since the number of the real neighbouring cells reported to the network would go down from 6 to 5.